1. Field of the Invention
The invention relates to a sensor for sensing rotational and linear displacement and more particularly for a sensor used in a vehicle with a pneumatic suspension having a height control system. In another aspect, the invention relates to a height control system having a sensor for detecting changes in the vehicle ride height and controlling the pneumatic suspension in response to the sensor output to adjust the vehicle height. In yet another aspect, the invention relates to a trailing arm suspension having a rotatably mounted arm whose movement is damped by an airbag in combination with a height control sensor that detects changes in the vehicle ride height relative to a reference ride height based on the rotation of the arm and correspondingly controls the pneumatic pressure within the airbag to adjust the vehicle height.
2. Related Art
Pneumatic or pressurized-air height control systems are known and commonly used in heavy-duty vehicles, such as semi/tractor-trailers. A common implementation of such a height control system is a trailing arm suspension. The trailing arm suspension comprises a trailing arm having one end pivotally mounted to a bracket depending from a portion of the vehicle frame to permit rotation of the arm relative to the vehicle frame. The arm carries an axle on which the wheels of the vehicle are rotatably mounted. An air spring comprising an inflatable air bag is positioned between another portion of the arm and vehicle frame. Any changes in the vehicle ride height relative to a predetermined reference height pivots the arm, causing a corresponding compression or expansion of the airbag. The height of the vehicle can be controlled by adding or exhausting pressurized air from the air bag. Changes in the ride height typically occur during the loading and unloading of the vehicle.
Current trailing arm suspensions use a mechanical height control valve to control the introduction and exhaustion of pressurized air into the airbag. The height control valve comprises an inlet port fluidly coupled to a source of pressurized air on the vehicle, an airbag port fluidly coupled to the airbag, and an exhaust port fluidly coupled to the atmosphere. An actuating arm extends from the height control valve and is operably coupled to the trailing arm usually by an adjustable length rod. Rotation of the trailing arm correspondingly moves the arm of the height control valve. The arm of the height control valve moves an internal valve within the height control valve to either fluidly connect the pressurized air port to the air spring port or the air spring port to the exhaust port and thereby introduce or exhaust, respectively, pressurized air from the airbag. Setting the vehicle ride height for this type of mechanical height control valve is typically accomplished by adjusting the length of the rod connecting the trailing arm to the actuating arm of the height control valve.
A disadvantage of the current system is that the mechanical components are subject to damage during the normal operation of the trailing arm suspension or by technicians working on the suspension. If the connecting rod or the rotating arm of the height control valve are bent, it can alter the preset ride height of the height control valve and adversely effect the operation of the suspension. Additionally, if left unused for an extended period of time, generally greater than a 24 hour period, the height control valve can “freeze” in its current position, resulting in the failure of the height control valve to perform correctly until the responsible component of the height control valve is released.
It is desirable to have a trailing arm suspension and a height control sensor that is less susceptible to the hostile environment that degrades the performance of the current mechanical sensors for height control valves.